Graphite plays key role in COVID tests

The furious pace of scientific and academic research into ways to curb the spread of COVID-19 and other highly infectious diseases is yielding impressive results this summer.

Researchers say testing is key to understanding and controlling the spread of COVID-19, which has already taken more than four million lives around the world. However, current tests are limited by the tradeoff between accuracy and the time it takes to analyze a sample.

Another challenge of current COVID tests is cost. Most tests are expensive to produce and require trained personnel to administer and analyze them. Therefore, testing in low- and middle-income communities has been largely inaccessible, leaving individuals at greater risk of viral spread.

To address these drawbacks, researchers at the University of Pennsylvania have developed a new electrochemical test for the COVID-19 virus that outperforms other tests currently on the market. The new test uses graphite, the same mineral found in ordinary pencil lead.

A paper detailing the innovation was published July 27 in PNAS, the Proceedings of the National Academy of Science journal.

Faster, cheaper, easier

Using electrodes made from graphite, a team of scientists led by César de la Fuente from Penn's Machine Biology Group in Philadelphia has developed a test for the coronavirus that costs just $1.50 per unit, requires only 6.5 minutes to deliver results that are 100% accurate from saliva samples, and up to 88% accurate in nasal samples.

While de la Fuente's previous research highlights the invention of RAPID (Real-time Accurate Portable Impedimetric Detection prototype 1.0) – a COVID-19 testing kit that uses screen-printed electrodes – this new research presents LEAD (Low-cost Electrochemical Advanced Diagnostic), using the same concept as RAPID but with less expensive materials. De la Fuente's team reduced the cost from $4.67 per RAPID test to $1.50 per LEAD test just by changing the building material of the electrodes.

The new test uses easily assembled materials, including human angiotensin-converting enzyme 2, modified graphite leads, and a plastic vial. Additionally, no cross-reactivity with other viruses has been detected and the LEAD test displayed a viable shelf-life of 5 days when stored at 4 degrees Celsius (39.2 degrees Fahrenheit).

"Both RAPID and LEAD work on the same principle of electrochemistry," de la Fuente told reporters recently. "However, LEAD is easier to assemble, it can be used by anyone, and the materials are cheaper and more accessible than those of RAPID. This is important because we are using an abundant material, graphite – the same graphite used in pencils – to build the electrode to make testing more accessible to lower-income communities."

The researcher said LEAD's functionalization and sample diagnosis take less than a few hours and can be made for a fraction of some of the most inexpensive tests on the market. Future steps for LEAD are twofold.

"Currently, we are working to improve the technology and stability of our tests," said de la Fuente. "We will always be looking for ways to make the most effective version of LEAD, but we are also working to find industry partners and conduct more clinical studies to push the use of LEAD for COVID testing as soon as possible."

While COVID-19 is the top priority, de la Fuente said the tests can also detect other transmissible diseases, which will keep the research relevant in the future.

"Another area of future research for our test design is multiplexing, which will allow us to detect multiple viruses and bacteria in a sample," he said. "Once COVID is relatively controlled, we can use LEAD to detect the flu, herpes, bacterial infections, and even certain biomarkers."

LEAD's cost and time efficiency may help it become one of, if not the first, electrochemical COVID-19 tests on the market in the near future, and its fundamental process of sample detection could keep it on the market indefinitely.

The research was funded by the National Institutes of Health, the Nemirovsky Prize, and funds provided by the Dean's Innovation Fund from the Perelman School of Medicine at the University of Pennsylvania.

Graphene breakthrough

Researchers at the University of Illinois Chicago, meanwhile, have successfully used graphene, one of the strongest, thinnest known materials, to detect the SARS-CoV-2 virus responsible for COVID-19 in laboratory experiments. The researchers reported the discovery in mid-June, saying it could be a breakthrough in coronavirus detection, with potential applications in the fight against COVID and its variants.

In their experiments, the researchers combined sheets of graphene, which are more than 1,000 times thinner than a postage stamp, with an antibody designed to target the infamous spike protein on the coronavirus.

They then measured the atomic-level vibrations of these graphene sheets when exposed to COVID-positive and COVID-negative samples in artificial saliva. The sheets also were tested in the presence of other coronaviruses, like Middle East respiratory syndrome, or MERS-CoV.

The UIC researchers found the vibrations of the antibody-coupled graphene sheet changed when treated with a COVID-positive sample, but not when treated with a COVID-negative sample or with other coronaviruses. Vibrational changes, measured with a device called a Raman spectrometer, were evident in under five minutes.

The findings were published June 16 in the journal "ACS Nano."

"We have been developing graphene sensors for many years. In the past, we have built detectors for cancer cells and ALS. It is hard to imagine a more pressing application than to help stem the spread of the current pandemic," said Vikas Berry, professor and head of chemical engineering at the UIC College of Engineering and senior author of the paper.

"There is a clear need in society for better ways to quickly and accurately detect COVID and its variants, and this research has the potential to make a real difference," Berry said. "The modified sensor is highly sensitive and selective for COVID, and it is fast and inexpensive."

The study's co-author Garrett Lindemann, a researcher with Carbon Advanced Materials and Products, or CAMP, said, "The development of this technology as a clinical testing device has many advantages over the currently deployed and used tests."

Berry said that graphene has unique properties that make it highly versatile, making this type of sensor possible.

Graphene is a single-atom-thick layer of the mineral graphite, which is comprised of sp2 bonded carbon atoms arranged in a hexagonal or honeycomb lattice. Carbon atoms are bound by chemical bonds whose elasticity and movement can produce resonant vibrations, also known as phonons, which can be very accurately measured.

When a molecule like a SARS-CoV-2 molecule interacts with graphene, it changes these resonant vibrations in a very specific and quantifiable way.

"Graphene is just one atom thick, so a molecule on its surface is relatively enormous and can produce a specific change in its electronic energy," Berry said. "In this experiment, we modified graphene with an antibody and, in essence, calibrated it to react only with the SARS-CoV-2 spike protein. Using this method, graphene could similarly be used to detect COVID-19 variants."

The researchers said the potential applications for a graphene atomic-level sensor, from detecting COVID to ALS to cancer, continue to expand.